A vehicle such as an automobile has been conventionally mounted with a supercharged engine in which intake air sucked into the cylinder of the engine is supercharged by a turbocharger for the purpose of enhancing output power or reducing fuel consumption. Here, the turbocharger is a supercharger in which a turbine is rotated by the use of exhaust energy of the engine to drive a compressor mounted coaxially with this turbine to supercharge intake air. Hence, the turbocharger presents a problem that a boost pressure does not rise sharply in the low rotational speed range of the engine to lower an actual boost pressure to lower charging efficiency to thereby produce an insufficient improvement in the output of the engine.
For the purpose of solving this problem, a supercharging assist control system having a rotary motor built in a turbocharger (system for controlling a turbocharger provided with a motor) has been developed (for example, refer to JP-7-019063A). Moreover, a system for controlling a turbocharger provided with a motor, in which an electrically operated compressor for rotating and driving a compressor by a rotary motor is additionally mounted on a common turbocharger, has been also developed. Here, a rotary motor used for an electrically operated assist turbo-system is mounted on a turbine shaft. Then, when the torque of the engine needs to be increased, for example, when high load is applied to the engine in a low rotational speed range such as in the case of climbing up a long uphill, power is supplied from a battery to the rotary motor via a power conversion unit to electrically drive the turbocharger (motoring), which assists the supercharging operation of the compressor to thereby increase a boost pressure. Then, when there is a margin of exhaust energy, the rotary motor is rotated and driven by the turbine torque to regenerate electricity to thereby charge the battery.
For this reason, the power conversion unit is provided with a DC-DC converter for boosting direct current from the battery, an inverter for inverting the boosted direct current into alternating current of a specified frequency to variably control the rotational speed of the rotary motor, and a rectifier circuit for rectifying the alternating current outputted from the rotary motor to direct current. Here, the DC-DC converter can also lower the direct current voltage outputted from the rectifier circuit to produce a specified battery voltage. Here, in both of the above-mentioned systems, when the torque of the engine needs to be increased, the supercharging operation of the compressor needs to be assisted to increase the boost pressure and hence there is a case where the power conversion unit is continuously used for a long time. In this case, there is a possibility that the internal temperature of the power conversion unit increases to accelerate the deterioration of the respective electronic components of the power conversion unit to thereby cause the failure of the respective electronic components of the power conversion unit.
Then, in the power control device of a turbocharger provided with a motor, which is described in JP-7-019063A, the power conversion unit is provided with a temperature sensor, and the temperature of electronic components mounted in the power conversion unit (internal temperature of the power conversion unit) is measured by this temperature sensor. A temperature signal outputted from the temperature sensor is compared with a determination value (for example, a high limit and a reference temperature), and according to comparison result, operating the rotary motor is stopped so as to prevent the rotary motor from being failed by overheating or a maximum current applied to the electronic components of the power conversion unit is limited.
However, in the power control device of a turbocharger provided with a motor, a rotary motor is rotated at a high speed when the torque of the engine needs to be increased and is arranged in a place of high temperature of an engine room. Hence, there is presented a problem that the rotary motor under high temperature cannot be avoided from deterioration and failure.
Then, the following can be thought: that is, a temperature sensor is mounted on the motor case of the rotary motor; a motor temperature is measured by the temperature sensor; a temperature signal outputted from the temperature sensor is compared with a determination value; and according to the comparison result, energizing through the heating component of the rotary motor is stopped or power supplied to the heating components of the rotary motor is limited so as to prevent failure caused by overheating (to prevent the heating component from being overheated).
However, in the case of this system, because the temperature sensor is mounted on the motor case, the heating component of the rotary motor, in particular, the temperature of a motor winding part (for example, armature winding or field winding) is not found correctly and hence a determination value for protecting the motor from being overheated needs to be set at a lower value. Hence, it is impossible to make the most of the performance of the rotary motor, that is, supercharging assist performance. Moreover, because the temperature sensor needs to be added, there is presented the problem of increasing wirings and cost. Furthermore, there is presented a problem that when a break in a wiring between the temperature sensor and the controller and the faulty mounting of the temperature sensor occur, it is impossible to prevent the rotary motor from being overheated.